Youll need a course with at least one existing grade item in it.
Go to the gradebook to the categories and items screen. Add a new grade item (theres a button beneath the categories and items table).
Once its created click the calculator icon in the new grade item's row.
In the ID Numbers section enter some names for the existing grade items. For example, firstitem and otherassignment. Check that they save without error.
Enter a formula using the ID numbers. for example =[ [firstitem] ]+[ [otherassignment] ]
Check that it saves without error. It will complain about an invalid formula if it's not correct.

Adrian Greeve
added a comment - 07/May/13 6:02 AM Hello,
This is a simple enough fix. Looking further at the code I see that we are using $idnumbers as an array so this should have been using optional_param_array().
No problems found. Submit for integration when ready.

Andrew Davis
added a comment - 13/May/13 1:57 AM Sol, I'm not sure what trouble you're having as this seems to resolve the issue for me. I've created 2.3 and 2.4 versions. Putting this up for integration.

I think that perhaps your problem might be unrelated to this issue. This patch is to remove the notice that appears when adding id numbers to grade items in the calculated grade settings. If you could give a more detailed explanation as to what your problem is we can determine if we can help your here, or direct you to create a new issue.

Adrian Greeve
added a comment - 13/May/13 5:19 AM Hello Sol,
I think that perhaps your problem might be unrelated to this issue. This patch is to remove the notice that appears when adding id numbers to grade items in the calculated grade settings. If you could give a more detailed explanation as to what your problem is we can determine if we can help your here, or direct you to create a new issue.
Thanks.